- integrate KIWIImageBuilder approach better:
  + move __getBaseWorkingDir, __createWorkingDir, __cleanupWorkingDir
    and __getBaseWorkingDir into the KIWIContainerBuilder. They are
    specific to the creation of lxc containers
  + delete __provideResults from KIWIImageBuilder. what happens with
    the result belongs to KIWIImageCreator not to the plain builder
  + add __createBuildDir to the KIWIImageBuilder constructor.
    the creation of the intermediate build directory is done
    by the base class for all image builds. The result of the
    build is created there
  + integrate KIWIImageBuildFactory better into the KIWIImageCreator
    the first build is based on KIWIImageBuildFactory. If the image
    can't be build by this factory the image is build calling a
    creation function from the KIWIImage space. In the future more
    and more image creation code will be moved from KIWIImage to
    KIWIImageBuildFactory
  + format creation, build result archiving and move of result into
    user specified target directory applies to a successfull build
    no matter if it was done by the KIWIImageBuildFactory or by a
    image creation function from the KIWIImage space
  + adapt unit tests
- eliminate getImageVersion_legacy method from XML
- fixed oem-silent-install and oem-silent-verify options. They
  were not evaluated in __updateDescriptionFromChangeSet_legacy